Table Of Contents

Modems in a Mobile Environment

This chapter describes roaming with external wireless modems.

Roaming with External Wireless Modems

General Packed Radio Service/Code Division Multiplex Access (GPRS/CDMA) modems provide the mobile access router with a Layer 2 roaming interface. The Mobile IP stack allows layer 3 roaming IP connectivity for the mobile access router. External modems are connected to a serial interface of the mobile access router. The serial interface should be running in asynchronous mode. Figure 13-1 shows a sample scenario in which the serial port of the mobile access router is connected to a CDMA modem.

Figure 13-1 Modem to Mobile Access Router Connection

The mobile access router supports the following modems:

•Airlink Raven

•AnyDATA I-Port

•Wavecom

Configuration Example

The example configurations shown in Figure 13-2 and Figure 13-3 demonstrate the router's ability to roam back and forth between 802.11b and Cellular technologies. The browser-based applications and video move dynamically to and from the different technologies. The 1X technology provides approximately 60 Kbps. The Nextel provides approximately 20 Kbps, but the network provides for static IP addresses and private links back to the headquarters. Implementing IPsec VPN in the mobile access router provides a secure connection back to the headquarters through 802.11b technology.

Initialization Strings

Recommended initialization strings for some common modems are provided in Table 13-1, but be aware that Cisco does not warrant that they are suitable or current. When in doubt, refer to the modem vendor's documentation or technical support.